Cell cryopreservation composition and cryopreservation method

ABSTRACT

This composition can be easily added when cryopreserving cells and improves cell viability. 1 volume % of the composition containing 0.01 wt % to 20 wt % of a sophorose lipid is added just before or up to 6 hours before cryopreservation and cells are stored. This composition can improve cryopreservation cell viability as it reduces freezing damage to cells. With this composition, cells can be stored without using DMSO and blood serum. This is a simple and inexpensive storage method as it does not require fine control of the freezing rate during cell cryopreservation.

TECHNICAL FIELD

The present invention relates to cryopreservation compositions that are used to cryopreserve cells, and cryopreservation methods using the same.

BACKGROUND ART

Cell cryopreservation is widely used as an essential technique to prevent cell degeneration due to passaging, prevent contamination with bacteria associated with passaging, transport cells, etc. However, it is known that, in the process of freezing cells, water in and out of the cells turns into ice crystals and the ice crystals damage the cells (Non-Patent Document 1). It I therefore desired to protect cells from damage during freezing and thawing and to cryopreserve cells while maintaining their properties.

In common cryopreservation, cells are typically suspended in a culture solution containing bovine serum etc. with a cryoprotectant for protecting the cells from damage from ice crystals, and the cell suspension thus obtained is placed in a cryotube etc., cooled, and eventually cryopreserved at a cryogenic temperature of −80° C. or −196° C. The cryoprotectant is 5 to 20% of dimethyl sulfoxide (DMSO), glycerin (Gly), ethylene glycol (EG), propylene glycol (PG), etc. (Patent Documents 1, 2). The most effective and most common cryoprotectant among these is DMSO (Non-Patent Document 2). However, a cryopreservation solution containing DMSO as a cryoprotectant does not have satisfactory preservation efficiency, and it cannot necessarily be said that this cryopreservation solution sufficiently inhibits ice crystal formation.

There are a cryopreservation solution further containing polyether to enhance the effect of DMSO (Patent Document 3), a cryopreservation solution containing a fructan to enhance the cytoprotective effect (Patent Document 4), and a cryopreservation solution containing carboxylated polylysine to enhance the stem cell storing effect (Patent Document 5). However, it cannot be said that these cryopreservation solutions sufficiently inhibit ice crystal formation. There is a concern about cytotoxicity of residual polyether, and a less toxic cryopreservation solution is desired. Moreover, since the cryopreservation solution contains as high as 30% of fructan, this is economically disadvantageous, and it is also difficult to remove fructan after preservation. Cell preservation using carboxylated polylysine focuses only on stem cells and is therefore not so versatile. Furthermore, since carboxylated polylysine is a polypeptide, there is also a concern about its impact on cell functionality etc. The above cryopreservation solutions are thus not always satisfactory with respect to cell preservation. Accordingly, a low-toxic cryopreservation solution is desired which can preserve all the cells.

CITATION LIST Patent Documents

-   PATENT DOCUMENT 1: Japanese Patent No. 5940975 -   PATENT DOCUMENT 2: Japanese Unexamined Patent Publication No.     2001-247401 -   PATENT DOCUMENT 3: Japanese Unexamined Patent Publication (Japanese     Translation of PCT Application) No. H10-511402 -   PATENT DOCUMENT 4: Japanese Unexamined Patent Publication No.     2012-235728 -   PATENT DOCUMENT 5: Japanese Patent No. 5630979 -   PATENT DOCUMENT 6: Japanese Unexamined Patent Publication No.     2016-160244

Non-Patent Documents

-   NON-PATENT DOCUMENT 1: Mazur, Am. J. Physiol., 247:C125-142, 1984 -   NON-PATENT DOCUMENT 2: Kovelock J E and Bioshop M W H, Nature     183:1394-1395, 1959

SUMMARY OF THE INVENTION Technical Problem

Since current cryopreservation methods do not sufficiently inhibit ice crystal formation and do not sufficiently protect cells from freezing damage, development of a novel low-toxic cryopreservant is desired.

Solution to the Problem

The inventors intensively studied to solve the above problems and found that a sophorose lipid (SL) can inhibit ice crystal formation and can easily reduce freezing damage to cells. Based on these findings, the inventors found that adding 0.01 wt % to 20 wt % of SL to a cell culture solution before cryopreservation improves cell preservation efficiency and that adding 0.01 wt % to 20 wt % of SL during cryopreservation reduces DMSO toxicity. The inventors also found that mixing 1 wt % to 50 wt % of a polyhydric alcohol with 0.01 wt % to 20 wt % of SL improves cell viability after cryopreservation without adding DMSO. The present invention provides the following:

[1] A composition that contains 0.01 wt % to 20 wt % of a sophorose lipid and improves cell viability after cryopreservation. [2] The composition of [1], containing 5 wt % to 10 wt % of dimethyl sulfoxide (DMSO). [3] The composition of [1] or [2], containing 1 wt % to 50 wt % of a polyhydric alcohol. [4] The composition of [3], containing at least one of glycerin, ethylene glycol, and propylene glycol as the polyhydric alcohol. [5] A cell cryopreservation method in which 1 volume % of the composition of [1] is added to a cell culture medium just before or up to 6 hours before cryopreserving cells. [6] A cell cryopreservation method in which 10 volume % to 99 volume % of the composition of any of [2] to [4] is added to a cell culture medium when cryopreserving cells.

Advantages of the Invention

Addition of SL can reduce freezing damage to cells. As a result, a certain level or higher of cell viability can be obtained even without relying on the effects of DMSO and serum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A)-(H) are micrographs showing inhibition of ice crystal formation, where (A) is ultrapure water, (B) is 10% SL, (C) is 0.1% SL, (D) is 10% DMSO, (E) is 10% Gly. (F) is 10% PG, (G) is 10% EG, and (H) is 10% APG.

FIG. 2 is a graph showing expression of cell markers.

FIG. 3 (A)-(K) are micrographs showing cell morphology, where (A) is 0.2% SL+30% Gly, (B) is 0.2% SL+20% Gly, (C) is 0.2% SL+15% Gly, (D) is 0.1% SL+30% Gly, (E) is 0.1% SL+20% Gly, (F) is 0.1% SL+15% Gly, (G) is 0.05% SL+30% Gly, (H) is 0.05% SL+20% Gly, (I) is 0.05% SL+15% Gly, (J) is 30% Gly, and (K) is 20% DMSO.

DESCRIPTION OF EMBODIMENTS

SL is a low-toxic glycolipid biosurfactant and is a fermentation product produced by fermentation of yeast. SL has the following effects. When added before freezing cells (addition before freezing), SL is taken into the cells and inhibits ice crystal formation within the cells. When added upon freezing, SL inhibits ice crystal formation outside the cells. SL used in the following experimental examples and examples was prepared according to the description in Japanese Unexamined Patent Publication No. 2016-160244. SL adjusted to pH 6 to 8 was used. A pH adjuster is an alkaline agent, an acid, etc.

A polyhydric alcohol is glycerin, ethylene glycol, propylene glycol, etc. and is preferably propylene glycol.

Cells for a cell preservation solution are animal and plant cells such as somatic cells, cancer cells, cell lines, and stem cells.

The cell preservation solution is also similarly applicable to tissues formed by cells, organs, and individuals such as animals and plants. The cell preservation solution can be expected to keep plant- and animal-derived foods fresh.

The freezing and thawing methods using the present invention are not particularly limited. Fine temperature control need not necessarily be performed during freezing, and common slow freezing and rapid thawing may also be used.

Experimental Examples: Ice Crystal Formation Inhibiting Composition and Ice Crystal Formation Inhibiting Effect

Each of the compositions shown in Table 1 was mixed with Dulbecco's modified Eagle's medium (DMEM), which is a medium most commonly used for cell preservation, at a volume ratio of 7:3. Each sample was dispensed into a 15 ml centrifuge tube (Thermo Scientific BioLite) and cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order, and the appearance of each sample was visually observed after cooling at −80° C. for 10 minutes.

TABLE 1 Ice Crystal Formation Composition Inhibiting Effect Example 1 33 wt % SL ◯ Example 2 0.033 wt % SL ◯ Example 3 33 wt % APG ◯ Example 4 0.033 wt % APG ◯ Example 5 distilled water or ultrapure water X Example 6 33 wt % DMSO Δ ◯: No ice crystal seen Δ: Small ice crystals seen X: Large ice crystals seen APG: alkyl polyglucoside* (* PLANTACARE 200UP, BASF Japan Ltd.)

The results in Table 1 show that Examples 1 to 4 inhibited ice crystal formation more than Examples 5 and 6 did.

Ultrapure water solutions with compositions as shown in Table 2 were prepared. Each sample was frozen by a cooling stage of a scanning probe microscope (AFM5000/AFM5300, Hitachi High-Tech Science Corporation) and observed with an optical microscope. This Lest was conducted with support of Nanotechnology Open Facilities in Osaka University. Each obtained image was analyzed using image analysis software (OLYMPUS cellSens Standard) to measure the area per ice crystal.

TABLE 2 Composition Ice Crystal Area (μm²) Ultrapure Water 307.3 10 wt % SL 1.6 0.1 wt % SL 1.8 10 wt % DMSO 4.2 10 wt % Gly 4.8 10 wt % PG 3.3 10 wt % EG 4.4 10 wt % APG 1.8 * SL: sophorose lipid Gly: glycerin EG: ethylene glycol PG: propylene glycol APG: alkyl polyglucoside

FIG. 1, (A)-(H) are micrographs showing inhibition of ice crystal formation, where (A) is ultrapure water, (B) is 10 wt % SL, (C) is 0.1 wt % SL, (D) is 10 wt % DMSO, (E) is 10 wt % Gly, (F) is 10 wt % PG, (G) is 10 wt % EG, and (H) is 10 wt % APG. As shown in FIGS. 1B and 1C, the solutions containing SL inhibited ice crystal formation regardless of whether the SL content was 0.1 wt % or 10 wt %. As shown in FIGS. 1, (A), (D), (E), (F) and (G), ultrapure water and the solutions containing a substance other than SL did not sufficiently inhibit ice crystal formation. As shown in FIG. 1. (H), however, the solution containing APG that is the same glycolipid surfactant as SL inhibited ice crystal formation.

EXAMPLES

[1. Effect of SL Addition Upon Culturing Before Cryopreservation (Human Normal Fibroblasts, Serum-Containing Medium)]

Human normal fibroblasts (KURABO) were sown on a 6-well plate at 3.2×10⁴ cells/ml and cultured for 48 hours. After culturing, the culture medium was removed, and a 5 wt % SL aqueous solution was diluted with DMEM containing fetal bovine serum to prepare a 0.05 volume % SL solution. The solution thus prepared was added to the cultured cells. After culturing for a predetermined time, the viable cell count was measured by trypan blue staining (viable cell count before freezing). The remaining cells were suspended in 1 ml of a 10% DMSO/fetal bovine serum-containing DMEM solution in CRYOGENIC VIAL (Sansyo Co., Ltd.), and the cell suspension thus obtained was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., the cell suspension was rapidly thawed at 37° C., and the viable cell count was measured by trypan blue staining (viable cell count after thawing). The remaining cell suspension was sown on a 6-well plate and the cells were cultured for 72 hours. The viable cell count after culturing was measured by trypan blue staining (viable cell count after culturing).

The viability upon thawing and the proliferation rate were calculated by the following equations.

Viability upon thawing (%)=viable cell count after thawing/total cell count after thawing×100

Proliferation rate (%)=viable cell count after culturing/viable cell count after thawing×100

TABLE 3 Viability Upon Proliferation Sample Thawing (%) Rate (%) Comparative Not added 86.7 467.8 Example 1 Example 1 Added 1 hr before 91.4 570.5 cell recovery Example 2 Added 4 hrs before 90.1 753.5 cell recovery Example 3 Added 6 hrs before 94.9 741.6 cell recovery

The results in Table 3 show culturing with SL added 1 to 6 hours before cell cryopreservation resulted in higher cell viability upon thawing and a higher cell proliferation rate than culturing with no SL added.

Not only the viability upon thawing but also the viability before and after freezing were examined. Specifically, human normal fibroblasts (KURABO) were sown on a 10 mm dish at 4.0×10⁴ cells/ml and cultured for 72 hours. After culturing, a 5 wt % SL aqueous solution was diluted to prepare a 0.05 volume % SL solution, and the solution thus prepared was added to the cultured cells. After culturing for a predetermined time, the resultant cell suspension was sown on a 96-well plate at 2.0×10⁴ cells/ml, and the cells were cultured for 6 or 72 hours. Absorbance was then measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance before freezing). The remaining cells were suspended at a cell density of 4.0×10⁵ cells/ml, and the cell suspension thus prepared and 20% DMSO were mixed at a volume ratio of 1:1 in CRYOGENIC VIAL (Sansyo Co., Ltd.). The resultant cell suspension was placed in a freezing container. BICELL (Nihon Freezer Co., Ltd.), and cooled at −80° C. After overnight storage, the cell suspension was rapidly thawed at 37° C., 100 μl of the cell suspension was sown on a 96-well plate, and the cells were cultured for 6 or 72 hours. Absorbance was then measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance after cryopreservation).

The viability before and after freezing and the proliferation rate were calculated by the following equations.

Viability before and after freezing (%)=absorbance after cryopreservation (6-hour culture)/absorbance before freezing (6-hour culture)

Proliferation rate (%)=absorbance after cryopreservation (72-hour culture)/absorbance before freezing (72-hour culture)

TABLE 4 Viability Proliferation Sample (%) Rate (%) Comparative Not added 60.7 93.4 Example Example 27 Added 1 hr before cell recovery 77.4 102.0 Example 28 Added 4 hrs before cell recovery 79.2 98.8 Example 29 Added 6 hrs before cell recovery 82.7 96.4

The results in Table 4 show that culturing with SL added 1 to 6 hours before cell cryopreservation resulted in higher cell viability before and after freezing and a higher cell proliferation rate than culturing with no SL added.

[2. Effect of SL Addition Upon Culturing Before Cryopreservation (Human Normal Fibroblasts, Serum-Free Medium)]

Human normal fibroblasts (KURABO) were sown on a 6-well plate at 3.2×10⁴ cells/ml and cultured for 48 hours. After culturing, the culture medium was removed, and a 5 wt % SL aqueous solution was diluted with a DMEM medium to prepare a 0.05 volume % SL solution. The solution thus prepared was added to the cultured cells. After culturing for 6 hours, the viable cell count was measured by trypan blue staining (viable cell count before freezing). The remaining cells were suspended in 1 ml of a 10% DMSO/DMEM solution in CRYOGENIC VIAL (Sansyo Co., Ltd.), and the cell suspension thus obtained was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., the cell suspension was rapidly thawed at 37° C. and the viable cell count was measured by trypan blue staining (viable cell count after thawing).

The viability before and after freezing was calculated by the following equation.

Viability before and after freezing (%)=viable cell count after thawing/viable cell count before freezing×100

TABLE 5 Viability Before and Sample After Freezing (%) Comparative Example 2 Not added 74.3 Example 4 Added 6 hrs before cell 97.0 recovery

The results in Table 5 show that culturing with SL added 6 hours before cell cryopreservation resulted in higher cell viability before and after freezing than culturing with no SL added.

[3. Effect of SL Addition Upon Culturing Before Cryopreservation (Mesenchymal Stem Cells, Serum-Free Medium)]

Mesenchymal stem cells (Lonza) were sown on a 6-well plate at 3.2×10⁴ cells/ml and cultured for 48 hours. After culturing, the culture medium was removed, and a 5 wt % SL aqueous solution was diluted with an MSCGM-CD medium to prepare a 0.05 volume % SL solution. The solution thus prepared was added to the cultured cells. After culturing for 6 hours, the viable cell count was measured by trypan blue staining (viable cell count before freezing). The remaining cells were suspended in 1 ml of a 10% DMSO/MSCGM-CD medium in CRYOGENIC VIAL (Sansyo Co., Ltd.), and the cell suspension thus obtained was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., the cell suspension was rapidly thawed at 37° C., and the viable cell count was measured by trypan blue staining (viable cell count after thawing).

The viability before and after freezing was calculated by the following equation.

Viability before and after freezing (%)=viable cell count after thawing/viable cell count before freezing×100

TABLE 6 Viability Before and Sample After Freezing (%) Comparative Not added 84.3 Example 3 Example 5 Added 6 hrs before cell recovery 94.5

The results in Table 6 show that culturing with SL added 6 hours before cell cryopreservation resulted in higher cell viability before and after freezing than culturing with no SL added.

[4. Effect of SL Addition without Culturing Before Cryopreservation (Human Normal Fibroblasts, Serum-Containing Medium)]

The viable cell count of human normal fibroblasts (KURABO) was measured by trypan blue staining (viable cell count before freezing). The cells were suspended in DMEM containing fetal bovine serum. Each of the samples shown in Tables 7 and 8 and the cell suspension were mixed at a volume ratio of 3:7 in CRYOGENIC VIAL (Sansyo Co., Ltd.), and each of the resultant cell suspensions was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., each cell suspension was rapidly thawed at 37° C., and the viable cell count was measured by trypan blue staining (viable cell count after thawing). Each of the remaining cell suspensions was sown on a 6-well plate and the cells were cultured for 72 hours. The viable cell count after culturing was measured by trypan blue staining (viable cell count after culturing).

The viability before and after freezing and the proliferation rate was calculated by the following equations.

Viability before and after freezing (%)=viable cell count after thawing/viable cell count before freezing×100

Proliferation rate (%)=viable cell count after culturing/viable cell count after thawing×100

TABLE 7 Viability Before and After Concentrations and Components Freezing (%) Example 7 0.033 wt % SL + 3.3 wt % Gly 5.9 Example 8 0.033 wt % SL + 16.5 wt % Gly 39.8 Example 9 0.033 wt % SL + 33 wt % Gly 73.9 Example 10 0.033 wt % SL 5.4 Example 11 0.033 wt % SL + 3.3 wt % PG 7.1 Example 12 0.033 wt % SL + 16.5 wt % PG 71.4 Example 13 0.033 wt % SL + 33 wt % PG 100.0 Comparative 33 wt % DMSO 84.8 Example 4 Comparative 33 wt % Gly 68.9 Example 5 Comparative 33 wt % PG 54.9 Example 6 Gly: glycerin (concentrated glycerin, made by Acidchem) PG: propylene glycol (made by ADEKA CORPORATION)

The results in Table 7 show that Examples 12 and 13 had high cell viability and Example 13 had higher viability than Comparative Examples 4 to 6.

TABLE 8 Proliferation Concentrations and Components Rate (%) Comparative 2.2% carboxylated polylysine* 69.2 Example 7 Example 14 0.033 wt % SL + 16.5 wt % PG 484.6 (*CryoScarless DMSO-Free, made by BioVerde)

Example 14 had a higher proliferation rate than Comparative Example 7.

Human normal fibroblasts were sown on a 96-well plate at 2.0×10⁴ cells/ml and cultured for 6 or 72 hours. After culturing, absorbance was measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance before freezing). The remaining cells were suspended at 4.0×10⁵ cells/ml in DMEM containing fetal bovine serum. Each of the compositions shown in Table 9 and the cell suspension were mixed at a volume ratio of 1:1 in CRYOGENIC VIAL (Sansyo Co., Ltd.). Each of the resultant cell suspensions was placed in a freezing container, BICELL (Nihon Freezer Co., Ltd.), and cooled at −80° C. After overnight storage, each cell suspension was rapidly thawed at 37° C., 100 μl of each cell suspension was sown on a 96-well plate, and the cells were cultured for 6 or 72 hours. Absorbance was then measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance after cryopreservation).

The viability and the proliferation rate were calculated by the following equations.

Viability (%)=absorbance after cryopreservation (6-hour culture)/absorbance before freezing (6-hour culture)

Proliferation rate (%)=absorbance after cryopreservation (72-hour culture)/absorbance before freezing (72-hour culture)

TABLE 9 Concentrations and Components Viability (%) Proliferation Rate (%) Comparative Example 14 20 wt % DMSO 66.5 95.9 Comparative Example 15 30 wt % Gly 59.5 60.8 Comparative Example 16 20 wt % Gly 53.0 54.7 Comparative Example 17 15 wt % EG 65.4 70.3 Comparative Example 18 15 wt % PG 77.6 81.6 Comparative Example 19 CELLBANKER*¹ 86.6 101.3 Comparative Example 20 Reprocryo*² 81.4 95.5 Comparative Example 21 CryoScarless*³ 65.3 24.4 Comparative Example 22 BAMBANKER*⁴ 83.5 91.9 Comparative Example 23 CP-5E*⁵ 73.9 89.7 Comparative Example 24 CP-1*⁶ 34.8 75.4 Example 30 0.02 wt % SL + 30 wt % Gly 84.6 97.3 Example 31 0.02 wt % SL + 30 wt % EG 72.1 95.9 Example 32 0.02 wt % SL + 30 wt % PG 54.2 85.8 Example 33 0.086 wt % SL + 10 wt % Gly + 71.9 102.8 10 wt % PG + 6.6 wt % EG Example 34 0.1 wt % SL + 30 wt % Gly 82.8 94.9 Example 35 0.1 wt % SL + 30 wt % EG 52.7 88.8 Example 36 0.11 wt % SL + 15 wt % Gly + 72.8 104.8 15 wt % PG Example 37 0.11 wt % SL + 15 wt % Gly + 71.5 102.1 10 wt % EG *¹STEM-CELLBANKER DMSO Free GMP Grade (Manufacturer: ZENOAQ RESOURCE CO., LTD., Use: human IPS and ES cells) *²ReproCryo DMSO Free RM (Manufacturer: ReproCELL Inc., Use: human IPS and ES cells) *³CryoScarless DMSO-Free (Manufacturer: BioVerde, Use: unspecified) *⁴BAMBANKER (Manufacturer: GC LYMPHOTEC Inc., Use: human-derived cells) *⁵CP-5E (Manufacturer: KYOKUTO PHARMACEUTICAL INDUSTRIAL CO., LTD, Use: human IPS and ES cells) *⁶CP-1 (Manufacturer: KYOKUTO PHARMACEUTICAL INDUSTRIAL CO., LTD, Use: hematopoietic stem cells)

The results in Table 9 confirmed that the examples of the present invention had high cell viability and high cell proliferation rates.

[5. Impact of DMSO Addition on SL Addition without Culturing Before Cryopreservation (Rat Skeletal Muscle Myoblasts, Serum-Containing Medium)]

The viable cell count of rat skeletal muscle myoblasts (JCRB9081 L6) was measured (viable cell count before freezing). The remaining cells were suspended in DMEM containing fetal bovine serum. Each of the compositions shown in Table 7 and the cell suspension were mixed at a volume ratio of 3:7 in CRYOGENIC VIAL (Sansyo Co., Ltd.), and each of the resultant cell suspensions was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C. each cell suspension was rapidly thawed at 37° C., and the viable cell count was measured (viable cell count after thawing).

The viability was calculated by the following equation.

Viability before and after freezing (%)=viable cell count after thawing/viable cell count before freezing×100

As a property of myoblasts, cytokines (VEGF) in the culture supernatant after 5 days of culture was quantified by ELISA.

TABLE 10 Viability Before and Concentrations and Components After Breezing (%) VEGF (pg/ml) Comparative Example 8 33 wt % DMSO 38.0 2100 Example 15 3.3 wt % SL + 33 wt % DMSO 10.0 3900 Example 16 0.33 wt % SL + 33 wt % DMSO 35.0 3400 Example 17 0.033 wt % SL + 33 wt % DMSO 48.0 2400

The results in Table 10 show that Examples 15 to 17 had higher cell viability than Comparative Example 8 (10 wt % DMSO only) and that Examples 15 to 17 had larger amounts of VEGF than Comparative Example 8 (10 wt % DMSO only). This means that the impact of freezing on cell properties was smaller in the examples than in the comparative example.

[6. Impact of DMSO Addition on SL Addition without Culturing Before Cryopreservation (Human Skeletal Muscle Myoblasts, Serum-Containing Medium)]

The viable cell count of human skeletal muscle myoblasts (from patients) was measured (viable cell count before freezing). The remaining cells were suspended in DMEM containing fetal bovine serum. Each of the compositions shown in Table 11 and the cell suspension were mixed at a volume ratio of 3:7 in CRYOGENIC VIAL (Sansyo Co., Ltd.), and each of the resultant cell suspensions was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., each cell suspension was rapidly thawed at 37° C. and the viable cell count was measured (viable cell count after thawing).

The viability was calculated by the following equation.

Viability Before and after Freezing (%)=Viable Cell Count after Thawing/Viable Cell Count Before Freezing×100

TABLE 11 Viability Before and Concentrations and Components After Freezing (%) Comparative 33 wt % DMSO 81.5 Example 9 Example 18 33 wt % SL + 33 DMSO 90.7 Example 19 3.3 wt % SL + 33% DMSO 93.4 Example 20 0.33 wt % SL+ 33% DMSO 95.5 Example 21 0.033 wt % SL + 33% DMSO 93.6 DMSO: made by FUJIFILM Wako Pure Chemical Corporation

The results in Table 11 show that Examples 18 to 21 had higher cell viability than Comparative Example 9 (10 wt % DMSO only).

The impact of DMSO addition on SL addition regarding viability upon thawing was examined by using Caco-2 cells and a serum-containing medium. Specifically, the viable cell count of Caco-2 cells (human colon adenocarcinoma) was measured (viable cell count before freezing). The remaining cells were suspended in DMEM containing fetal bovine serum. Each of the compositions shown in Table 10 and the cell suspension were mixed at a volume ratio of 1:1 in CRYOGENIC VIAL (Sansyo Co., Ltd.), and each of the resultant cell suspensions was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., each cell suspension was rapidly thawed at 37° C., and the viable cell count was measured (viable cell count after thawing).

The viability was calculated by the following equation.

Viability upon thawing (%)=viable cell count after thawing/total cell count after thawing×100

TABLE 12 Viability Upon Concentrations and Components Thawing (%) Comparative 20 wt % DMSO 86.0 Example 25 Example 38 0.02 wt % SL + 20 wt % DMSO 90.0

The results in Table 12 show that the example of the present invention had higher viability upon thawing than the comparative example (20 wt % DMSO only).

[7. Impact of PG Addition on SL Addition without Culturing Before Cryopreservation (Human Normal Fibroblasts, Serum-Free Medium)]

The viable cell count of human normal fibroblasts (KURABO) was measured by trypan blue staining (viable cell count before freezing). The cells were suspended in serum-free DMEM. Each of the samples shown in Table 13 and the cell suspension were mixed at a volume ratio of 3:7 in CRYOGENIC VIAL (Sansyo Co., Ltd.), and each of the resultant cell suspensions was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., each cell suspension was rapidly thawed at 37° C., and the viable cell count was measured by trypan blue staining (viable cell count after thawing).

The viability before and after freezing and the viability after proliferation were calculated by the following equations.

Viability before and after freezing (%)=viable cell count after thawing/viable cell count before freezing×100

Viability after proliferation (%)=viable cell count after culturing/total cell count after culturing×100

TABLE 13 Viability Before and Viability After Concentrations and Components After Freezing (%) Proliferation (%) Example 22 0.033 wt % SL + 16.5 wt % PG 50.2 76.5 Example 23 0.033 wt % SL + 33 wt % PG 60.2 100.0 Comparative Example 10 33 wt % PG 34.4 95.8 Comparative Example 11 33 wt % DMSO 61.0 97.1

The results in Table 13 show that Examples 22 and 23 had higher viability before and after freezing than Comparative Example 10 and that Example 23 had higher viability after proliferation than Comparative Examples 10 and 11.

[8. Impact of PG Addition on SL Addition without Culturing Before Cryopreservation (Mesenchymal Stem Cells, Serum-Free Medium)]

The viable cell count of mesenchymal stem cells (Lonza) was measured by trypan blue staining (viable cell count before freezing). The cells were suspended in an MSCGM-CD medium. Each of the samples shown in Table 14 and the cell suspension were mixed at a volume ratio of 3:7 in CRYOGENIC VIAL (Sansyo Co., Ltd.), and each of the resultant cell suspensions was cooled at 4° C. for 5 minutes, −20° C. for 20 minutes, and −80° C. in this order. After overnight storage at −80° C., each cell suspension was rapidly thawed at 37° C., and the viable cell count was measured by trypan blue staining (viable cell count after thawing).

The viability before and after freezing was calculated by the following equation.

Viability before and after freezing (%)=total cell count after thawing/total cell count before freezing×100

TABLE 14 Viability Before and Concentrations and Components After Freezing (%) Example 24 0.033 wt % SL + 3.3 wt % PG 88.1 Example 25 0.033 wt % SL + 16.5 wt % PG 90.3 Example 26 0.033 wt % SL + 33 wt % PG 92.6 Comparative 33 wt % PG 83.9 Example 12 Comparative 33 wt % DMSO 89.2 Example 13

The results in Table 14 show that Examples 24 to 26 had higher viability before and after freezing than Comparative Example 12 and that Examples 25 and 26 had higher viability before and after freezing than Comparative Example 13.

The impact of addition of a polyhydric alcohol other than PG on SL addition without culturing before cryopreservation (mesenchymal stem cells, serum-containing medium) was also examined. Specifically, mesenchymal stem cells (Lonza) were sown on a 96-well plate at 2.0×10⁴ cells/ml and cultured for 6 or 72 hours. After culturing, absorbance was measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance before freezing). The remaining cells were suspended at 4.0×10⁵ cells/ml in DMEM containing fetal bovine serum. Each of the compositions shown in Table 15 and the cell suspension were mixed at a volume ratio of 1:1 in CRYOGENIC VIAL (Sansyo Co., Ltd.). Each of the resultant cell suspensions was placed in a freezing container, BICELL (Nihon Freezer Co., Ltd.), and cooled at −80° C. After overnight storage, each cell suspension was rapidly thawed at 37° C., 100 Itl of each cell suspension was sown on a 96-well plate, and the cells were cultured for 6 or 72 hours. Absorbance was then measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance after cryopreservation). Cellular gene (mRNA) expression before and after freezing was also evaluated.

The viability and the proliferation rate were calculated by the following equations.

Viability (%)=absorbance after cryopreservation (6-hour culture)/absorbance before freezing (6-hour culture)

Proliferation rate (%)=absorbance after cryopreservation (72-hour culture)/absorbance before freezing (72-hour culture)

TABLE 15 Concentrations and Components Viability (%) Proliferation Rate (%) Example 39 0.01 wt % SL + 20 wt % Gly 60.6 71.6 Example 40 0.02 wt % SL + 30 wt % Gly 37.7 67.6 Example 41 0.02 wt % SL + 30 wt % EG 30.6 62.5 Example 42 0.1 wt % SL + 30 wt % Gly 54.3 83.7 Example 43 0.1 wt % SL + 20 wt % Gly 71.9 74.3 Example 44 0.2 wt % SL + 20 wt % Gly 51.7 73.9 Comparative Example 26 20 wt % DMSO 44.7 30.7 Comparative Example 27 30 wt % Gly 55.1 51.9 Comparative Example 28 20 wt % Gly 54.9 34.7

The results in Table 15 show that the examples of the present invention had high viability before and after freezing and high proliferation rates before and after freezing, but the viability before and after freezing was slightly lower in the example in which 0.2 wt % of SL was added.

Gene expression of cells was examined for the example of 0.02 wt % SL+30 wt % Gly, the example of 0.02 wt % SL+30 wt % EG, and the example of 0.1 wt % SL+30 wt % Gly of the present invention and the comparative example of 20 wt % DMSO. The results are shown in FIG. 2. CD34 and CD73 are markers of mesenchymal stem cells. There is almost no variation in CD34 and CD73 between the example of the present invention and the unfrozen cells, and the example of the present invention is considered to maintain properties as mesenchymal stem cells. Moreover, there is variation in c-myc, which is an oncogene acting as an accelerator of cell division, between Comparative Example 26 (20 wt % DMSO) and the unfrozen cells, but there is almost no variation in c-myc between the example of the present invention and the unfrozen cells, and the example of the present invention is considered to hardly affect mesenchymal stem cells.

[9. Cytotoxicity of Compositions (Mesenchymal Stem Cells)]

Mesenchymal stem cells (Lonza) were sown on a 96-well plate at 2.0×10⁴ cells/ml and cultured for 72 hours. After culturing, the culture medium was removed, and each of the compositions shown in Table 16 was diluted to the concentration(s) shown in Table 16 with DMEM not containing fetal bovine serum. Each of the solutions thus prepared was added to the cultured cells. After culturing for 48 hours, absorbance was measured with Cell Counting Kit-8 (DOJINDO LABORATORIES).

The viability was calculated by the following equation.

Viability (%)=absorbance after exposure to composition/absorbance before treatment

TABLE 16 Concentrations and Components Viability (%) Comparative Example 29 15 wt % Gly 62.5 Comparative Example 30 10 wt % Gly 76.7 Comparative Example 31 7.5 wt % Gly 87.8 Comparative Example 32 5 wt % Gly 88.0 Example 45 0.025 wt % SL + 10 wt % Gly 84.0 Example 46 0.025 wt % SL + 7.5 wt % Gly 94.3 Example 47 0.025 wt % SL + 5 wt % Gly 95.5 Example 48 0.025 wt % SL 104.3 Example 49 0.05 wt % SL + 15 wt % Gly 76.0 Example 50 0.05 wt % SL + 10 wt % Gly 88.4 Example 51 0.05 wt % SL + 7.5 wt % Gly 94.3 Example 52 0.05 wt % SL + 5 wt % Gly 91.3 Example 53 0.05 wt % SL 100.8 Example 54 0.075 wt % SL + 15 wt % Gly 80.4 Example 55 0.075 wt % SL + 10 wt % Gly 89.8 Example 56 0.075 wt % SL + 7.5 wt % Gly 97.3 Example 57 0.075 wt % SL + 5 wt % Gly 97.9 Example 58 0.075 wt % SL 105.1 Example 59 0.1 wt % SL + 15 wt % Gly 68.9 Example 60 0.1 wt % SL + 10 wt % Gly 82.1 Example 61 0.1 wt % SL + 7.5 wt % Gly 85.0 Example 62 0.1 wt % SL+ 5 wt % Gly 90.6 Example 63 0.1 wt % SL 96.7 Comparative Example 33 10 wt % DMSO 75.2

The results in Table 16 show that the combination of SL and glycerin is less toxic to mesenchymal stem cells than DMSO.

[10. Results of Culturing without Removing Cryopreservation Composition after Thawing (Mesenchymal Stem Cells)]

Mesenchymal stem cells (Lonza) were sown on a 96-well plate at 2.0×10⁴ cells/ml and cultured for 6 or 72 hours. After culturing, absorbance was measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance before freezing). The remaining cells were suspended at 4.0×10⁵ cells/ml in DMEM containing fetal bovine serum. Each of the compositions shown in Table 17 and the cell suspension were mixed at a volume ratio of 1:1 in CRYOGENIC VIAL (Sansyo Co., Ltd.). Each of the resultant cell suspensions was placed in a freezing container, BICELL (Nihon Freezer Co., Ltd.), and cooled at −80° C. After overnight storage, each cell suspension was rapidly thawed at 37° C., 100 μl of each cell suspension was sown on a 96-well plate without removing the composition, and the cells were cultured for 6 hours. Absorbance was then measured with Cell Counting Kit-8 (DOJINDO LABORATORIES) (absorbance after cryopreservation).

The viability and the proliferation rate were calculated by the following equations.

Viability (%)=absorbance after cryopreservation (6-hour culture)/absorbance before freezing (6-hour culture)

TABLE 17 Viability Observed Concentrations and Components (%) Morphology Example 64 0.2 wt % SL + 30 wt % Gly 33.9 Δ Example 65 0.2 wt % SL + 20 wt % Gly 41.7 ∘ Example 66 0.2 wt % SL + 15 wt % Gly 28.0 ∘ Example 67 0.1 wt % SL + 30 wt % Gly 28.2 Δ Example 68 0.1 wt % SL + 20 wt % Gly 48.6 ∘ Example 69 0.1 wt % SL + 15 wt % Gly 48.7 ∘ Example 70 0.05 wt % SL + 30 wt % Gly 31.9 Δ Example 71 0.05 wt % SL + 20 wt % Gly 35.0 ∘ Example 72 0.05 wt % SL + 15 wt % Gly 52.7 ∘ Comparative 30 wt % Gly 20.7 Δ Example 34 Comparative 20 wt % DMSO 10.8 x Example 36 ∘: the number of bonded cells was 80% or more of the number of bonded unfrozen cells Δ: the number of bonded cells was 30 to 80% of the number of bonded unfrozen cells x: the number of bonded cells was 30% or less of the number of bonded unfrozen cells

The morphology of the cells of the examples and the comparative examples was observed with a microscope. FIG. 3, (A)-(K) are micrographs showing cell morphology, where (A) is 0.2 wt % SL+30 wt % Gly, (B) is 0.2 wt % SL+20 wt % Gly, (C) is 0.2 wt % SL+15 wt % Gly, (D) is 0.1 wt % SL+30 wt % Gly, (E) is 0.1 wt % SL+20 wt % Gly, (F) is 0.1 wt % SL+15 wt % Gly, (G) is 0.05 wt % SL+30 wt % Gly, (H) is 0.05 wt % SL+20 wt % Gly, (I) is 0.05 wt % SL+15 wt % Gly. (J) is 30 wt % Gly, and (K) is 20 wt % DMSO. The results in Table 17 show that the combination of SL and glycerin is less toxic to mesenchymal stem cells than DMSO. The results in FIGS. 3A to 3K show that more satisfactory cell morphology was obtained by the combination of SL and glycerin than by DMSO.

[11. Effect of SL Addition in Frozen Storage of Vegetables or Fruits]

Aqueous solutions with the compositions shown in Tables 18, 19, and 20 were prepared, and each food (cucumber, spinach, apple) was immersed in 100 g of each aqueous solution for 30 minutes. After immersion, the foods were dried with a paper towel and frozen at −20° C. After overnight storage, the foods were thawed at 37° C. and their appearance and texture were scored according to the following criteria.

(Criteria)

3: No difference from before freezing 2: Different from before freezing 1: Significantly different from before freezing

TABLE 18 Composition Appearance Taste Texture Example 73 20 wt % SL 3.0 2.4 3.0 Example 74 10 wt % SL 3.0 3.0 3.0 Example 75 5 wt % SL 3.0 3.0 3.0 Example 76 1 wt % SL 3.0 2.5 2.4 Example 77 0.1 wt % SL 3.0 2.1 1.8 Comparative Example 37 Water 3.0 1.8 1.2

TABLE 19 Composition Appearance Taste Texture Example 78 10 wt % SL 3.0 3.0 3.0 Example 79 5 wt % SL 3.0 3.0 3.0 Example 80 1 wt % SL 3.0 3.0 2.8 Example 81 0.1 wt % SL 3.0 2.8 2.1 Example 82 0.01 wt % SL 3.0 2.3 1.9 Comparative Example 38 Water 3.0 1.6 1.2

TABLE 20 Composition Appearance Taste Texture Example 83 20 wt % SL 2.8 2.5 3.0 Example 84 10 wt % SL 3.0 3.0 3.0 Example 85 1 wt % SL 3.0 3.0 2.7 Example 86 0.1 wt % SL 3.0 2.6 2.0 Comparative Example 39 Water 3.0 1.8 1.4

The results in Tables 18, 19, and 20 confirmed that vegetables or fruits immersed in an SL-containing solution before frozen storage had a good taste and texture when thawed after frozen storage.

[12. Effect of SL Addition in Frozen Storage of Seafood or Meat]

Aqueous solutions with the compositions shown in Tables 21 and 22 were prepared, and each food (tuna, liver) was immersed in 100 g of each aqueous solution for 30 minutes. After immersion, the foods were dried with a paper towel, weighed (weight before freezing), and frozen at −20° C. After overnight storage, the foods were thawed at 37° C. Their appearance was observed, and their drip amounts were also measured. The appearance was scored according to the following criteria.

(Criteria)

3: No difference from before freezing 2: Different from before freezing 1: Significantly different from before freezing

The drip amount (weight after removal of food) was measured and drip loss was calculated by the following equation. When a food is thawed, ice in its cells melts into water, which flows out of damaged cells. This water is called drip.

Drip loss (%)=drip amount/weight before freezing×100

TABLE 21 Composition Appearance Drip Loss (%) Example 87 20 wt % SL 2.6 16.7 Example 88 10 wt % SL 3.0 16.7 Example 89 5 wt % SL 3.0 20.1 Comparative Example 40 Water 1.8 23.4

TABLE 22 Composition Appearance Drip Loss (%) Example 90 20 wt % SL 3.0 1.5 Example 91 10 wt % SL 3.0 1.8 Example 92 5 wt % SL 3.0 2.0 Comparative Example 41 Water 2.1 2.2

The results in Tables 21 and 22 confirmed that immersing seafood or meat in an SL-containing solution before frozen storage reduces drip loss. 

1. A composition comprising 0.01 wt % to 20 wt % of a sophorose lipid, wherein, when added to cells, the composition improves cell viability after cryopreservation.
 2. The composition of claim 1, comprising 5 wt % to 10 wt % of dimethyl sulfoxide (DMSO).
 3. The composition of claim 1, comprising 1 wt % to 50 wt % of a polyhydric alcohol.
 4. The composition of claim 3, comprising at least one of glycerin, ethylene glycol, and propylene glycol as the polyhydric alcohol.
 5. A composition comprising a sophorose lipid and a polyhydric alcohol, wherein the composition does not contain dimethyl sulfoxide (DMSO), and wherein the composition, when added to cells, improves cell viability after cryopreservation.
 6. The composition of claim 5, wherein the polyhydric alcohol is glycerin, and the cells are stem cells.
 7. The composition of claim 6, wherein the stem cells are mesenchymal stem cells.
 8. A cell cryopreservation method comprising adding a 1 volume % of the composition of claim 1 to cells in a cell culture medium just before or up to 6 hours before cryopreserving the cells.
 9. A cell cryopreservation method comprising adding a 10 volume % to 99 volume % of the composition of claim 2 to cells in a cell culture medium when cryopreserving cells. 